He burst through the back door of the Dunkin’ Donuts shortly after 10 p.m. Wednesday with a black hoodie pulled tight over his face and a gun in his hand. He ordered the employees to get down on the ground, robbed the register and a cash box, and then disappeared into the night.

The bad guy was gone in seconds, leaving behind frightened employees and lingering questions: Who is robbing all the Dunkin’ Donuts, and is there a reason that the Canton-based coffee giant, one of New England’s best known brands, is the target?

Since March, there have been at least 19 robberies of Dunkin’ Donuts locations in Massachusetts, the latest at a store on Needham Street in Newton, also robbed in July.

Others have occurred in Westwood, West Roxbury, Walpole, Canton, Norton, Avon, Newton, North Attleborough, Plainville, Norwood, Easton, and Raynham, according to a list provided by Dunkin’ Donuts. There was also a similar robbery at a Dunkin’ Donuts in Nashua in September.

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“It’s easy to look at them and say they’re all related, but the truth is that it could be an individual, a copy cat, or a group of people working together,” said Newton police Lieutenant Bruce Apotheker. “But the person has managed to get away so far, so until we catch them and question them, there’s no way to know why anybody does anything.”

Police in 13 municipalities are now involved in investigations. Dunkin’ Donuts has upped a reward for information leading to an arrest from $2,500 to $10,000.

The robberies have some Dunkin’ workers and customers a bit on edge. And wondering.

In Newton Thursday, customers leaving the Needham Street location that had been hit the night before were confused as to why someone was picking on their beloved Dunkies.

“Dunkin’ is a big thing in Boston,” said Rachel Block of Mission Hill. “I don’t like it. It’s as if somebody were to talk bad about the Red Sox.”

Others speculated that Dunkin’ represented an easy target, with cash on hand and light security.

“Everyone runs on Dunkin’, right?” Ali Gualtieri of Brookline said as she left the store with her coffee.

Police reports on the holdups follow a similar pattern, both in the suspect’s description and his method. Witnesses have described the suspect as about 5 feet 6 inches tall, dressed in dark clothing, with a slim or medium build. The suspect is usually described as a white or Hispanic male, though his face is obscured by a mask or a hoodie.

In every case, the suspect has brandished a gun or a knife, and he has frequently worn gloves. All the robberies have occurred at night on a weekday, and all but one have occurred between 7 p.m. and 11:30 p.m.

No one has been harmed in the robberies, and the suspect flees on foot and disappears, police said. Authorities would not disclose how much money has been taken.

‘If I’m a Dunkin’ employee, I’m looking over my shoulder.’

So far, investigators are reluctant to declare a connection between the 19 robberies, but Boston police have said that a string of five robberies at three Dunkin’ locations in West Roxbury between March and September are related.

In surveillance footage released from a July heist in West Roxbury, the suspect enters through a side door, orders employees to the ground, makes his way to the cash register at the drive-through window, quickly hits a few buttons on the register to make it open, then stuffs the cash in his pocket and dives out the drive-through window. The entire clip lasts 29 seconds.

Nashua police Lieutenant Denis Linehan said it is difficult to explain why the coffee shop chain has been targeted so aggressively but said the proximity of the shops to highways or other quick means of escape could be a possible reason. Six of the locations that have been hit are either on or near a major thoroughfare.

He also raised the possibility the suspect could be a former employee who knows company security procedures and staffing levels at that time of night.

“We had a series of Subway robberies,” Linehan said, referring to the chain of sandwich shops. “In that case, it happened to be a former employee who knew the ins and outs.”

Dunkin’ Donuts released a statement saying that its restaurants are owned and operated by individual franchisees who are responsible for making their own decisions with regard to security procedures. Newton police were alerted to the latest robbery via a panic button.

At Upper Falls Liquors, next door to the Dunkin’ Donuts, manager Mike O’Connell said police had checked the store’s surveillance cameras and come up empty, but told him it was probably an inside job. “They said it seemed like he knew exactly where to go, where to turn,” O’Connell said.

That was the surmise of Jim Anderson of Wellesley, who was leaving the Needham Street location Thursday afternoon. “This sounds like an inside job for this guy, the Dunkin’ Bandit, the Coffee Crook, whatever you want to call him,” Anderson said. “All I can say is that if I’m a Dunkin’ employee, I’m looking over my shoulder.”

This is not the first time that local Dunkin’ Donuts have been the target of a series of robberies. In 2011, Canton police arrested two brothers, charging them with more than 30 break-ins at Dunkin’ Donuts locations while the stores were closed.

Billy Baker can be reached at william.baker@globe.com. Follow him on Twitter @billy_baker.

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